Given the endless amounts of street lights that are positioned across our cities in order to provide adequate lighting for improved safety within the community, there has become a requirement that as there are so many individual street lamps, the amount of maintenance and power consumption for the street light needs to be as minimal as possible.
Therefore it follows that the street light controller responsible for activating the luminaire for the lamp should include the most appropriate components, not only from a point of view of power consumption and energy savings, but also potentially conflicting requirements of trying to minimise the cost and the frequency of servicing such street lights.
Conventionally street light controllers utilised electro-mechanical devices and switches but the suitability of such controllers are now being called into significant question as they are characterised with poor energy efficiency, hard initial start up which degrades the life expectancy of the lamp and they also have associated problems in relation to maintenance and potential for damage by power surges and so forth.
More recently electronic solid state street lighting controllers have entered the marketplace that provide opportunity for significant power savings compared to the conventional electro-mechanical devices referred to above and they also do not suffer relay contact wear and tear.
More recently electronic control devices such as TRIACs are being implemented as part of the street light controller in order to manipulate some inherent benefits alternating current provides from the mains power supply.
Using a TRIAC conduction of the AC wave form is not possible at the zero crossing point, meaning that there is a turning on and off of the TRIAC every time the mains crossing point is reached depending on the frequency of the supplied mains power.
A conventional way to overcome this problem has involved the use of electronic controlled systems that drive the gate of the TRIAC through a continuous DC input into the gate of the TRIAC, so that when a zero crossing occurs the TRIAC maintains conduction and the lamp remains powered.
Nonetheless effectively what this means is that once darkness has been detected and the lamp is required to be turned on, a continuous DC input into the gate of the TRIAC is required so that powering is still taking place at the zero crossing intervals of the AC mains supply and no lamp flickering results. This is a waste of energy as effectively the continuous DC input into the gate of the TRIAC is only driving the TRIAC at these zero cross over intervals, and for the majority of the AC wave signal the continuous DC input into the gate of the TRIAC plays no part in keeping the lamp powered as the TRIAC maintains its own conduction outside the zero crossing intervals.
In order to compensate for the zero crossings that are occurring 100 or 120 times per second on AC mains supply of 50 or 60 Hz, the gate of the TRIAC is being fed a continuous DC signal. The continuous on state of the DC signal throughout the entire phase of each AC cycle results in more power consumption.
As stated above there is a continuous requirement now to try and introduce all possible power savings so as to minimise the amount of energy each individual street light consumes and also at the same time to limit the amount of servicing required given the kinds of costs involved In maintaining such street lights.
Therefore it would be particularly advantageous to have a control system in place that can recognise and synchronise zero crossing points in either an inductive or capacitive environment, and provide a single pulse signal to the gate that drives the TRIAC only during zero crossing intervals.